Are you sure this is what you want here, or is this just a copy-paste from aliases.erb?  According to the man page you reference:

       The input format for the postmap(1) command is as follows:

       pattern result
              When pattern matches a mail address, replace it by the corresponding result.

       blank lines and comments
              Empty lines and whitespace-only lines are ignored, as are lines whose first non-whitespace character is a `#'.

       multi-line text
              A logical line starts with non-whitespace text. A line that starts with whitespace continues a logical line.